Apparatus for cleaning the elements of a cathode ray tube



K. PALAC June 6, 1967 APPARATUS FOR CLEANING THE ELEMENTS OF A CATHODE RAY TUBE Filed April 19. 1965 50 kv 0c.

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RANDOM GEN.

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Patented June a, 19s? 3,323,854 APPARATUS FOR CLEANING THE ELEMENTS OF A CATHODE RAY TUBE Kazimir Palac, Carpentersviile, Hi, assignor to Motorola, Inc., Franklin Park, 111., a corporation of Illinois Filed Apr. 19, H65, Ser. No. 448,968 3 Claims. (Cl. 316-1) This invention relates to the manufacture of cathode ray tubes of the type used in television receivers, and more particularly to a process for manufacturing said tubes which reduces the tendency for arcing among the electrodes thereof.

A cathode ray tube may operate with a potential difference of the order of 24,000 volts among its electrodes. In a tri-beam color tube, the three electron gun structures are positioned in the neck of the tube in closely spaced relation and the beams from the guns are deflected by a common deflection field. Furthermore, in such tubes adapted for a wide angle beam deflection, for example 90 or more, electron guns are particularly close spaced in order to deflect the beams by a deflection field of satisfactory uniformity through this relatively wide deflection angle. These considerations of close spacing and high voltages cause cathode ray tubes for producing color images to be particularly susceptible to arcing which can make noise that is disturbing to the user of the tube or which can cause current flow in the tube and its associated circuitry which damages the television receiver.

Such arcing has been found to be largely a function of foreign matter or contamination within the tube, and of mechanical imperfections in the construction of the electron guns of the tube. Such improvement in arcing characteristics can be achieved by carefully cleaning of the gun parts before they are assembled. Additionally, it is helpful to employ a high voltage are out to melt metal projections of the gun or stray particles of foreign matter within the tube, after the tube has been evacuated and sealed, so that these no longer tend to promote arcing.

Because a portion of the interior surface of the cathode ray tube neck is generally coated with conductive material which is connected to the anode portion of the electron gun, a problem may arise when the are out potential is established between the final anode of the electron gun and the other elements thereof. The other elements of the electron gun, such as the grid and cathode, are connected to pins which extend exteriorly of the tube. These pins are all interconnected by a plug during the are out process. The potential difference between the final anode and other elements of the gun may cause arcing exteriorly of the tube between the plug and pins connecting the other elements of the electron gun and the interior conductive coating which extends partly into the tube neck. Under some circumstances this can actually result in a hole being burned through the tube neck and loss of the vacuum established in the tube.

Accordingly, it is an object of this invention to provide an improved process for treating a cathode ray tube to reduce the tendency for arcing among the parts thereof.

It is another object of the invention to provide a process for causing destruction of foreign particles and constructional imperfections of an electron gun in a cathode ray tube which minimizes the danger of damage to the tube.

Still another object of the invention is to provide means for preventing exterior are over between the grid and cathode connectors and the conductive coating on the interior surface of the tube neck during the are out process.

A feature of the invention is the provision of a sleeve of insulating material having an annular interior member of resilient insulating material, which sleeve and interior member may he slipped over the outside of the neck of the tube to prevent exterior are over.

Another feature of the invention is a provision of such a sleeve device wherein the interior member is comprised of a tubular ring.

Still another feature of the invention is the provision of an are over preventing sleeve device as described which is secured to a test plug for the connector pins of the electron gun in a cathode ray tube.

Referring now to the drawing:

FIG. 1 is an elevational view, partially in section, showing a tri-beam shadow mask cathode ray tube for producing images in color and wherein a circuit for producing are out is shown schematically;

FIG. 2 is a sectional view of a part of the neck of the cathode ray tube of FIG. 1 with one electron gun in section and illustrating the test plug connection and the are over preventing sleeve device; and

FIG. 3 is a sectional view similar to FIG. 2 showing an alternative embodiment of the invention.

The invention comprises both a process and apparatus for treating a cathode ray tube to reduce the tendency for arcing among the parts thereof. The cathode ray tube has an electron gun contained within its neck including an anode portion and a grid portion. The grid portion is connected to a conductor protruding exteriorly of the neck through the end thereof, and the interior of the neck is partially coated with conductive material which is connected to the anode portion. A sleeve of insulating material having an annular interior member of resilient insulating mtaerial is slipped over the outside of the neck of the tube with the interior member engaging the neck and holdin the sleeve thereon. When the are out potential is applied to the anode portion with respect to the grid portion, the sleeve prevents are over exteriorly of the tube between the connector and the conductive coating. This prevents arc over damage to the tube envelope.

In FIG. 1, the tri-beam color cathode ray tube 10 includes connection pins 12, an insulator and male plug member 13, a neck section 14 and a funnel portion 16. Within the neck section there is an electron gun assembly 18 comprising three separate identical electron gun structures (one being 42, 44, 46', 50 in FIG. 3, e.g.) for producing three electron beams. The inside of the funnel portion 16 is coated with an aquadag coating 20, which is electrically connected to a portion of the gun structure 18 by means of the contacts 22. This aquadag coating extends a short distance along the inside surface of the neck section 14.

The forward or flared portion of the funnel 16 is joined to the faceplate panel 24 along a frit sealing line 26. Faceplate panel 24 includes a shadow mask structure 28 supported by means of spring clips 36 and mounting studs 32. which are melted into the side walls of the faceplate panel 24. The viewing screen 34 of the picture tube comprises phosphor coatings which emit colored light when impinged by electron beams from the gun structure 18. As will be understood by those familiar with the cathode ray tube art, screen 34 is composed of three complete sets of phosphors and one of the three electron beams passes through the apertures of the shadow mask structure 28 to strike only one set of the phosphor dots. The energization of the three different sets of phosphors in the screen 34 by the beams produces an image having a color depending upon the relative energization of the different phosphors which respectively produce light of red, green and blue color.

The tube 10 has a faceplate panel 24, which is preferably of rectangular configuration when viewed from the front, and the tube has a relatively wide deflection angle for the beams (for example, 90 or more) so that the overall length of the tube may be as short as possible and the receiver in which the tube is used may be compact. The deflection angle referred to, of course, concerns the angle through which the beams are swept in traveling across the screen 34.

In a tube of practical construction, the neck section 14 may be of the order of 1 /2 inches in diameter, so that the electron guns are closely spaced. Typical potentials applied to the electrodes of the gun structure, by the way of base pins 12 and the final anode connector 36, may be best considered by viewing FIG. 2. During the operation of a tube in a television receiver, the cathode electrode 4-0 may be operated at a DC potential of 260 volts, the first or control grid 42 may be operated at a DC potential of 130 volts, the second or screen grid 44 may be operated at a potential of 750 volts and the third or focus grid 46 may be operated at a potential of 5,000 volts. The potential of the screen 34, the aquadag coating 20, the convergence electrode structure 48 and the final anode member 50 may all be established at a potential of the order of 24 kv. Accordingly, it may be seen that various electrodes within neck 14 are at widely different potentials and in closely spaced relation, which can result in the production of damaging arcs. For example, the focus electrode 46 can arc over to the electrode 50.

One treatment which has been found effective to reduce the tendency for arcing within a television picture tube as described above is very thorough cleaning of the electron gun structure before it is sealed within the tube neck. Each of the three different guns, including the grids 42, 44, 46 and 50, may be of stainless steel which may include trace impurities on the surface or trace amounts of foreign matter introduced in handling and manufacture. Thus, chemical cleaning and even electro-mechanical cleaning of the gun structure prior to sealing within the tube can be very helpful in reducing the tendency for arcing. However, it should also be recognized that further particles of foreign matter may be introduced on the gun structure after it is assembled in the tube and that in spite of careful chemical cleaning there may be still an undesirable tendency for arcing in a'completely assembled tube. Thus, further provision for reducing arcing has been found necessary, particularly in the case of very closely spaced electron guns operating at high voltage in a color picture tube.

Considering the process at the time after the guns have been chemically cleaned and the tube is assembled with the guns in a tube neck which has been acid rinsed, the evacuated and sealed tube undergoes a getter flashing step. This is a known process involving the activation of gas absorbing material within the bulb of the tube to reduce residual quantities of gas remaining after vacuum pumping of the tube.

Following getter flashing, the parts of the electron gun are arced out for brief periods to burn or melt any sharp points or imperfections on the tri-gun assembly or any foreign particles which are capable of destruction in this manner. The arc out step is carried out with the grids 42 and 44, cathode 48 and focus electrode 46 all connected through their appropriate connector pins 12 to a 50 kv. AC peak random generator 37. Generator 37 may be of the Aesla type. The final anode connector 36 is connected to a 50 kv. DC source 39. The result is rapidly varying random voltage potential which may vary up to 100 kv. for brief instances. This is applied for about one minute to electrode 50 and convergence assembly 48 through a relatively high impedance source in order to limit arcing currents within the tube to a value which will not destroy the gun structure itself.

After the arc out step, the cathode is activated by applying a filament current considerably in excess of the normal operating current for high heating. The process of cathode activation is well known in the art and will not be described in detail here.

In order to apply the necessary potentials for the are out step previously described, a female plug 81 is attached to the connection pins 12 and male plug member 13. In order to establish an equal potential among the grids, focus electrode and cathode elements of the gun during the arc out step to prevent damage thereto, the pins are all interconnected by a conductive plate 82 on the face of plug 81. One or more of the pins may be connected through a contact 83 and conductor 84 to the peak random generator 37. Because of the extreme difference between the poten tial of the pins and plug connections and the potential of the inner aquadag coating 20 which extends into the neck of the tube, there is danger of arcing over between these elements exteriorly of the tube. Such arcing over can cause damage or even perforation of the envelope of the tube and consequent loss of the vacuum therein.

Accordingly, a sleeve 85, which may be of an acrylic plastic or other suitable insulating material, is provided with an annular recess 86, and an annular interior member, ring 87. Ring 87 is of resilient insulating material such as rubber and is just smaller than the neck diameter. Sleeve 85 and ring 87 are slipped over the neck 14 such that the ring 87 holds the sleeve 85 in position. The annular ring 87 prevents are over from the plug and pins to the inner aquadag coating interiorly of sleeve 85, while the sleeve itself is of a size which prevents any arc over exteriorly of the sleeve. A satisfactory proportion for the sleeve has been such that the sleeve extends partially over the convergence assembly 48 and terminates just beyond the end of the tube neck 14. In this manner the sleeve is of a size sufiicient to present a large enough air gap between pins 12 and coating 20 to prevent arcing therebetween.

In FIG. 3, an alternative form of the invention is shown. In this form of the invention, the sleeve 85 is secured to the plug 81 by means of screws 88. Such a construction enables placement of the sleeve and the test connector plug in a single operation to facilitate high quantity production. It will be noted from FIG. 3 that the annular interior member 91 in the recess 86 of sleeve 85 is of tubular cross-section and is slightly larger in cross-section than that shown in FIG. 3. Under some cir cumstances, this may be a more'desirable construction for the annular member in order to make it slide more readily over the neck 14.

It may, therefore, be seen that the invention provides an improved process for treating a cathode ray tube to reduce the tendency for arcing among the parts thereof. Arcing over from the connectors for the grid portions of the electron gun of the cathode ray tube and the conductive coating in the inner surface of the neck thereof is prevented by a sleeve device of insulating material. Damage to the tube envelope is thereby prevented.

I claim:

1. Apparatus for treating a cathode ray tube to reduce the tendency for arching among the parts thereof, the tube having a neck portion and an electron gun structure mounted therein, the gun structure having anode electrode means to be established at a high voltage anode potential during operation of the tube, and grid electrode means connected to conductor means protruding exteriorly of the neck portion, a conductive coating on the inner surface of the neck portion terminating at a selected point therein and electrically connected to said anode electrode means, said apparatus including in combination; a sleeve of insulating material, an annular interior member composed of resilient insulating material having an inner diameter less than the outer diameter of the neck portion of the tube and secured within said sleeve, said sleeve and said interior member being adapted to he slipped over the outside of the neck portion with the interior member being further adapted to engage the neck and hold the sleeve thereon, and means for applying an are producing potential substantially in excess of said high voltage anode potential to said anode electrode means with respect to said grid electrode means for causing destruction of foreign particles and constructional imperfections on said electron gun structure, the arc producing potential being suificiently high to present the possibility of arcing between the conductive coating and the conductor means thereby subjecting the tube to damage, said sleeve having length substantially as long as the distance between the point where the conductive coating terminates and the end of the neck portion whereby the conductor means protrudes, whereby arc-over between the conductor means and the conductive coating exteriorly of the tube is prevented.

2. The apparatus according to claim 1 wherein said means for applying an are producing potential include a conductive plug to be attached to the pin protruding exteriorly of the neck, with said sleeve being secured to said plug.

3. The apparatus according to claim 2 wherein said annular interior member comprises a tubular ring, said sleeve having an annular recess on the inner surface thereof, with said interior member being secured within said recess.

References Cited UNITED STATES PATENTS 2,583,029 1/1952 Towsend 3l61 3,208,811 9/1965 Mason 316-1 3,233,954 2/1966 Bailey et al. 316-1 RICHARD H. EANES, JR., Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,323,854 June 6, 1967 Kazimir Palac It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 46, for "aquadag" read Aquadag (A registered trademark of Acheson Industries, Inc. for their brand of colloidal graphite in water.) same column 2, line 48, column 3, line 19, and column 4, lines 12 and 25, for "aquadag", each occurrence, read Aquadag Signed and sealed this 5th day of November 1968.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

1. APPARATUS FOR TREATING A CATHODE RAY TUBE TO REDUCE THE TENDENCY FOR ARCHING AMONG THE PARTS THEREOF, THE TUBE HAVING A NECK PORTION AND AN ELECTRON GUN STRUCTURE MOUNTED THEREIN, THE GUN STRUCTURE HAVING ANODE ELECTRODE MEANS TO BE ESTABLISHED AT A HIGH VOLTAGE ANODE POTENTIAL DURING OPERATION OF THE TUBE, AND GRID ELECTRODE MEANS CONNECTED TO CONDUCTOR MEANS PROTRUDING EXTERIORLY OF THE NECK PORTION, A CONDUCTIVE COATING ON THE INNER SURFACE OF THE NECK PORTION TERMINATING AT A SELECTED POINT THEREIN AND ELECTRICALLY CONNECTED TO SAID ANODE ELECTRODE MEANS, SAID APPARATUS INCLUDING IN COMBINATION; A SLEEVE OF INSULATING MATERIAL, AN ANNULAR INTERIOR MEMBER COMPOSED OF RESILIENT INSULATING MATERIAL HAVING AN INNER DIAMETER LESS THAN THE OUTER DIAMETER OF THE NECK PORTION OF THE TUBE AND SECURED WITHIN SAID SLEEVE, SAID SLEEVE AND SAID INTERIOR MEMBER BEING ADAPTED TO BE SLIPPED OVER THE OUTSIDE OF THE NECK PORTION WITH THE INTERIOR MEMBER BEING FURTHER ADAPTED TO ENGAGE THE NECK AND HOLD THE SLEEVE THEREON, AND MEANS FOR APPLYING AN ARC PRODUCING POTENTIAL SUBSTANTIALLY IN EXCESS OF SAID HIGH VOLTAGE ANODE POTENTIAL TO SAID ANODE ELECTRODE MEANS WITH RESPECT TO SAID GRID ELECTRODE MEANS FOR CAUSING DESTRUCTION OF FOREIGN PARTICLES AND CONSTRUCTIONAL IMPERFECTIONS ON SAID ELECTRON GUN STRUCTURE, THE ARC PRODUCING POTENTIAL BEING SUFFICIENTLY HIGH TO PRESENT THE POSSIBILITY OF ARCING BETWEEN THE CONDUCTIVE COATING AND THE CONDUCTOR MEANS THEREBY SUBJECTING THE TUBE TO DAMAGE, SAID SLEEVE HAVING LENGTH SUBSTANTIALLY AS LONG AS THE DISTANCE BETWEEN THE POINT WHERE THE CONDUCTIVE COATING TERMINATES AND THE END OF THE NECK PORTION WHEREBY THE CONDUCTOR MEANS PROTUDES, WHEREBY ARC-OVER BETWEEN THE CONDUCTOR MEANS AND THE CONDUCTIVE COATING EXTERIORLY OF THE TUBE IS PREVENTED. 